Method and apparatus for the production of multichannel sound signals

ABSTRACT

In apparatus for reproducing multichannel sound signals, a system is provided for restoring a four-channel signal, derived from a two-channel sound source, to its two-channel condition, to produce two signals which are free of the additional two signals.

United States Patent Burkowitz 5] Nov. 11, 1975 [54] METHOD AND APPARATUS FOR THE 3.686.471 8/1972 Takahashi 179/1 60 PRODUCTION OF MULTlCHANNEL SOUND 3,745,254 7/1973 Ohta 179/1 60 SIGNALS 3,757,047 9/1973 lto 179/1 GO 3,786,193 1/1974 Tsurushima 179/] GO [75] Inventor: Peter Klaus Burkowitz lsernhagen-NBS, Gerniany OTHER PUBLICATIONS Extended Stereo S stem, Electronics World, Jan. [73] Assignee: gtzlgirazilm Gmbl-l, Hamburg, 1960 pp. 50, 156

y A Compatible StereoQuadra phonic (SQ) Record [22] Filed: June 4, 1973 System by B. Bauer, Journal ABS, Sept. 1971. [21] App]. No.: 366,554

Primary E.\'aminer-Kathleen H. Claffy Assistant Examiner-Thomas DAmico [3O] Forelgn Appllcatlon Data Attorney, Agent, or FirmHil1, Gross, Simpson, Van

June 7. 1972 Germany 2227705 Santen, Steadman, Chiara & Simpson [52] US. Cl. 179/1 GQ; 179/100.4 ST TRA v [51] Int. Cl. H04R 5/00 [57] ABS 53 Fie|d f Search 179715 B, 15 T, 1 GP, 1 G In apparatus for reproducing multichannel sound sig- 179 GQ 1 G A 1004 ST, 1001 TD nals, a system is provided for restoring a four-channel signal, derived from a two-channel sound source, to its 5 References Cited two-channel condition, to produce two signals which UNITED STATES PATENTS are free of the additional two signals.

3,584,154 6/1971 McShan 179/15 ET 3 Claims, lDrawing F gur METHOD AND APPARATUS FOR THE PRODUCTION'OF MULTICl-IANNEL SOUND SIGNALS BACKGROUND 1. Field of the Invention The present invention relates to a method and apparatus for producing multichannel sound signals, and more particularly, to asystem for restoringa properly balancedstereo signal from a four-channel signal derived from an original stereo signal.

2. The Prior The recent popularity of quadraphonic techniques in soundrecording reproduction has led .to the availability of ia number of four-channel recordings which are derived orig'inally from two-channel sources. The four-channel iec'ordings are derived" from the two original sound channels by modifying the normal left and right signals to produce two additional signals which are typically used as the left rear signal and the right rear signal, when the signals represent four corners of a quadrilateral. This is done in such a way that the fourchannel signal may be employed compatibly with normal stereo (two channel) equipment. When the four-' channel signals are reproduced with two-channel equipment, the two additional channels of the fourchannel signals are automatically combined on the normal left and right stereo channels to form composite left and composite right signals. This combination sometimes leads to a drastic deterioration in the sound produced by the two stereo channels, which is extremely undesirable.

SUMMARY OF THE PRESENT INVENTION It is a principal object of the present invention to provide a system for restoring the separation and balance of two-channel signals from four-channel signals which have been derived therefrom.

Another object of the present invention is to provide a simple means of accomplishing the aforesaid result.

These and other objects and advantages of the present invention will become manifest by examination of the following description and the accompanying drawmg.

In one embodiment of the present invention, there are provided means for producing four signals corresponding to the four channels of a quadraphonic sound source, means for mixing signals from two of the four channels to produce a reconstituted left two-channel signal, and means for mixing signals from the other two of said four channels to produce a reconstituted right two-channel signal.

BRIEF DESCRIPTION OF THE DRAWINGS Reference will now be made to the accompanying drawing, which is a functional block diagram of a system incorporating the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawing, a quadraphonic sound source is illustrated having four output lines, 1, 2, 3, and 4. The output line 1 is for the left front signal, the output line 2 is for the right front signal, the output line 3 is for the left rear signal, and the output line 4 is for the right rear signal. When quadraphonic reproduction is desired, these four outputsignals are applied respectively to the loudspeakers 6; =7, 8, and 9, in order to reproduce quadraphonic sound in the customary manner. v When it is desired to reproduce the original two- Channel stereo signal from which the quadraphonic signal is derived, the normal practice is to combine the signals on the left output lines 1 and 3 into a single outchannel signal is restored by mixing a portion of the signal available on the outputline 3 with the signal produced at the output line 1. 'A level control 10 is provided foi' selecting a portion of the signal available on a the output line 3 and connecting it to theloudspeaker I 6, 'in common with the output line 1 from the source 5.

A phase inverter 11 is interposed between the level control 10 and the loudspeaker 6,'.in order to'invert the phase ofthe'signal. 1 a, v f.

' A similar level control '12 i's provided for the right channel, and functions to mix a portion of the signal provided on the output line 4 with the signal provided on the output line 2 and to apply it to the loudspeaker 7. A phase inverter 13 is interposed between the level control 12 and the loudspeaker 7 to invert the phase of the signal.

It can be seen that, by means of the level controls 10 and 12, a selected portion of the signals on the output lines 3 and 4 may be added to the signals on the output lines 1 and 2. By operation of the phase inverters 11 and 13, the signals selected by the level controls 10 and 12 are, in effect, subtracted from the signals present on the outputs 1 and 2. When the level control 10 is adjusted so that the signal available at the output of the inverter 11 has components corresponding in amplitude to the components of the signal present on the output line 3, but opposite in phase, these components cancel each other out and form a new signal for application to the loudspeaker 6. Thus, the disturbing components are removed, restoring the original two-channel signal to the loudspeaker 6. The same is true of the signal applied to the loudspeaker 7 when the level control 13 is properly adjusted. If desired, the loudspeakers 8 and 9 may be disconnected, so that two-channel sound is produced only by the loudspeakers 6 and 7.

The phase inverters 1 l and 13 are preferably amplifiers having unity gain, with the output of the amplifiers being the inverse of the input, so that the frequency and phase relationship of the signals are not modified except to invert the phase thereof. The level controls 10 and 12 may take the form of T pads or L pads, or alternately, may comprise amplifiers having manually adjustable gains. Such devices are well known in the art and therefore need not be described in detail herein.

When a phase inversion of the signals derived from the output lines 3 and 4 is not desired, the inverters 11 and 13 may be omitted from the circuit. It is apparent that a great variety of different level signals may be provided by manipulation of the level controls 10 and 12, with the inclusion or omission of the phase inverters 11 and 13. The desired proportions of signals which are mixed in order to restore the original stereo signals are readily chosen by the operator, in accordance with his preferences.

What is claimed is:

l. A method of restoring two channel signals of a two-channel signal source by modifying the right front and left front signals of a four-channel source having individual channels for the left front signal, the right front signal, the left rear signal, and the right rear signal, such four signals having been derived from signals of said two-channel source, comprising the steps of: selecting a first portion of the left rear signal, inverting said first portion to produce a first inverted signal, and mixing only said first inverted signal with said left front signal for modifying said left front signal, selecting a second portion of the right rear signal, inverting said second portion to produce the second inverted signal, and mixing only said second inverted signal with said right front signal to produce a modified right front signal, whereby said modified left front and right front signals restore the signals of said two-channel source.

2. Apparatus for restoring two channel signals of a two-channel signal source by modifying the left front and right front signals of a four-channel source having separate channels for the left front signal, the right front signal, the left rear signal, and the right rear signal, such four signals having been derived from signals of said two-channel source, comprising means for selecting a first portion of said left rear signal, means for inverting said first portion to produce a first inverted signal, means for mixing said first inverted signal with said left front signal to produce a modified left front signal, means for selecting a second portion of said right rear signal, means for inverting said second portion to produce a second inverted signal, and means for mixing only said second inverted signal with said right front signal to produce a modified right front signal, whereby said modified left front and right front signals restore the signals of said two-channel source.

3. Apparatus according to claim 2, including a first variable resistor interconnected between said left front and left rear signals and a second variable resistor interconnected between said right front and right rear signals. 

1. A method of restoring two channel signals of a two-channel signal source by modifying the right front and left front signals of a four-channel source having individual channels for the left front signal, the right front signal, the left rear signal, and the right rear signal, such four signals having been derived from signals of said two-channel source, comprising the steps of: selecting a first portion of the left rear signal, inverting said first portion to produce a first inverted signal, and mixing only saId first inverted signal with said left front signal for modifying said left front signal, selecting a second portion of the right rear signal, inverting said second portion to produce the second inverted signal, and mixing only said second inverted signal with said right front signal to produce a modified right front signal, whereby said modified left front and right front signals restore the signals of said two-channel source.
 2. Apparatus for restoring two channel signals of a two-channel signal source by modifying the left front and right front signals of a four-channel source having separate channels for the left front signal, the right front signal, the left rear signal, and the right rear signal, such four signals having been derived from signals of said two-channel source, comprising means for selecting a first portion of said left rear signal, means for inverting said first portion to produce a first inverted signal, means for mixing said first inverted signal with said left front signal to produce a modified left front signal, means for selecting a second portion of said right rear signal, means for inverting said second portion to produce a second inverted signal, and means for mixing only said second inverted signal with said right front signal to produce a modified right front signal, whereby said modified left front and right front signals restore the signals of said two-channel source.
 3. Apparatus according to claim 2, including a first variable resistor interconnected between said left front and left rear signals and a second variable resistor interconnected between said right front and right rear signals. 